Optical shape sensing technology provides a 3D shape of an optical fiber. By integrating such a fiber in interventional devices, the shape of the device can be known, up to a point very close to the tip of the device. However, knowing the shape alone is not enough: the shape must be placed in the context of (i.e., registered with) pre-procedural and/or intra-procedural imaging data. Having a correct (i.e., accurate) registration between the coordinate system of the shape sensing system and the coordinate system of the pre-procedural and/or intra-procedural imaging data is essential for the usage and adoption of the shape sensing technology.
In one application for shape sensing technology, a shape sensing optical fiber may be integrated into a tether attached to a surgical instrument and/or the instrument itself and used for instrument tracking. The fiber-optically tracked device is introduced endovascularly or endoluminally. To use the optical fiber for instrument tracking, an initial registration of the optical fiber coordinate system to a reference coordinate system is required. The reference coordinate system may be, for example, a 3D anatomical model derived from segmenting a Cone Beam Computer Tomography (CBCT) scan.
If an initial registration between a virtual device from the shape sensing fiber and pre-procedural or intra-procedural imaging data is used, misalignment may be caused by various effects. These effects include: inaccuracy of the shape reconstruction (even slight errors in shape reconstruction can cause significant misalignment), launch point movement (if the launch point of the shape sensing system moves during a procedure the entire shape will move causing misalignment), and patient movement (any movement by the patient following an initial registration will cause misalignment of the shape sensing coordinates and the image data coordinates).
One solution to misalignment caused after or during the initial registration is to reregister the coordinate systems based on x-ray imaging in real time. However, x-ray exposure should be limited due to its harmful effects. Also, x-ray only provides a 2D projection of a device, and the exact relation of the 2D projection and the fiber inside the device is not known, but can only be estimated.